This invention relates to the use of multilayered containers having properties which are not obtainable in a single layered product.
Multilayered plastic containers are highly desirable whenever it is difficult to satisfy all of the requirements and specifications by using a single plastic.
For example, the low cost, easy formability, impact resistance and other desirable properties of polystyrene, polyvinyl chloride and polyolefins, especially polyethylene, would make them highly desirable containers for many commodities; however, for example, polyethylene does not have sufficient barrier or solvent resistance for many applications.
In instances of this kind, it has been attempted to provide a lined container, wherein the container wall is composed of more than one substance and thereby provide properties that no single plastic possesses.
However, heretofore the economical production of such containers was prohibitively difficult. In addition, certain combinations of properties presented considerable difficulties even in a composite container.
For example, it is highly desirable to obtain a plastic container having resistance to exposure to elevated temperatures, such as above 175.degree. F. and preferably above 220.degree. F., while at the same time having fluid barrier resistance, such as gas barrier resistance as resistance to the transmission of oxygen and carbon dioxide, or solvent resistance. In such instances, the non-barrier layer of the container may be made of relatively heat resistant plastics, e.g. polypropylene, SAN or polycarbonate. However, the barrier layer or layers, particularly oxygen-barriers, do not have adequate heat resistance. Hence, in containers of this type, it is known that when the container is exposed to elevated temperature conditions, as, for example, when filling with substances at such temperatures, the barrier material tends to melt, destroying the integrity and utility of the container. This is particularly significant since for many applications it is desirable to fill containers at elevated temperatures. The viscosity of the material being filled is lower at elevated temperatures, allowing more rapid filling. In addition, sterilization can be provided while or after the container is filled, either by material maintained at an elevated temperature during filling followed by prompt closure of the container preferably in an air tight manner, or by sterilizing in a retort after filling.
Accordingly, it is a principal object of the present invention to provide a method of obtaining a filled, fluid barrier resistant plastic container.
It is a particular object of the present invention to provide a method as aforesaid wherein the container is filled at temperatures in excess of 175.degree. F., or subsequently exposed to such temperatures, while retaining the barrier resistant characteristics thereof.
Further objects and advantages of the present invention will appear hereinbelow.